Electronic devices comprising active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes (OLEDs), organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices comprising organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.
An OLED may comprise a substrate carrying an anode, a cathode and one or more organic light-emitting layers between the anode and cathode. One or more organic charge transporting and/or one or more charge blocking layers may also be provided between the anode and cathode.
Holes are injected into the device through the anode and electrons are injected through the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of a light-emitting material combine to form an exciton that releases its energy as light.
Suitable light-emitting materials include small molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers include poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and polyarylenes such as polyfluorenes.
A light emitting layer may comprise a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant. For example, J. Appl. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton) and Appl. Phys. Lett., 2000, 77, 904 discloses a host material doped with a phosphorescent light emitting dopant (that is, a light-emitting material in which light is emitted via decay of a triplet exciton).
Formation of the one or more organic layers of an OLED may be by deposition of materials used to form those layers from a solution in a solvent followed by evaporation of the solvent. Examples of suitable solution processing methods include coating methods such as spin-coating or dip-coating and printing methods such as inkjet printing or roll-to-roll printing.
In devices comprising multiple organic layers, a first deposited organic layer may be rendered insoluble by crosslinking prior to deposition of a further organic layer by a solution processing method in order to prevent dissolution of the first deposited layer by the solvent used in formation by solution processing of the further organic layer. WO 2005/049689 discloses polymers comprising fluorene repeat units substituted with crosslinkable groups, including a double bond, a triple bond, a precursor capable of in situ formation of a double bond or a heterocyclic, addition polymerisable group. Benzocyclobutane (BCB) is disclosed as an exemplary crosslinkable group.
WO 2010/013723 discloses polymers comprising double bond groups and BCB groups.
Emission from more than one layer of an OLED, in particular to achieve white light emission, is disclosed in, for example, WO 2008/131750, DE 102007020644 and EP1390962 and SPIE (2004), 5519, 42-47.